The present invention relates to a developer composition for radiation-sensitive positive-working, negative-working, and reversible reprographic layers which, apart from a radiation-sensitive compound or radiation-sensitive combination of compounds, contain, as an essential constituent, a binder which is insoluble in water but soluble in aqueous-alkaline solutions. The developer composition exhibits particularly advantageous properties with respect to yield, developing speed and differentiation between image areas and non-image areas, and it does not tend to form foam or undesirable deposits. The developer composition provides a steep gradation when positive-working, negative-working, or reversible reproduction layers based on photopolymers or epoxides are processed. The invention is also directed to a process for developing reprographic layers with the developer composition.
Positive-working reprographic layers containing photosensitive compounds which, upon exposure, render the exposed areas soluble in an aqueous-alkaline developer solution, are known. In most cases, layers of this kind contain 1,2-quinonediazides as photosensitive compounds. Alkali-soluble resins, such as phenolic resins, may additionally be contained in these layers.
Layers containing a combination of a compound which forms an acid upon irradiation and an acid-cleavable compound, such as an orthocarboxylic acid derivative, a monomeric or polymeric acetal, an enol ether, a silyl ether and an acyliminocarbonate, are also known. Organic halogen compounds, in particular halomethyl-substituted s-triazines, are generally used as the radiation-sensitive, acid-eliminating compounds. Here, too, alkali-soluble resins are employed as binders.
Positive-working copying materials based on 1,2-quinonediazides, optionally in the presence of suitable additives, have also been used as negative-working copying materials, by subjecting the material to a certain sequence of processing steps. A positive-negative reversal process for a material based on acid-cleavable compounds instead of 1,2-quinonediazides is described in EP 082,463 (=U.S. Pat. No. 4,506,006).
Known reversal processes principally comprise the same sequence of processing steps, i.e., following exposure the printing plate is heated, cooled down, then post-exposed without an original and finally developed with an aqueous-alkaline developer. For practical application of the reversal process, safe performance of the individual process steps and reliable reproducibility of the results within narrow limits are of vital importance.
Negative-working, radiation-sensitive systems include combinations of ethylenically unsaturated monomers and photoinitiators and combinations of epoxide compounds and substances which upon irradiation eliminate a strong acid. Combinations of the above systems are also known. These reprographic layers contain binders which are soluble in aqueous-alkaline systems, preferably polycondensates or polymers having lateral carboxyl groups.
A developer composition and a developing process for radiation-sensitive layers or, respectively, reproduction materials produced therefrom, must meet a number of requirements, in particular:
1. The yield of the developer solution should be high, i.e., the performance of the developer with regard to the reprographic layer should remain as constant as possible, even when the developer is loaded with an increasing amount of removed layer constituents, and the tone limit, i.e., that degree of loading of the developer where the layer is no longer removed completely from the substrate, should be as high as possible.
2. The developing process should be finished after a short period of action of the developer on the layer. This is of particular importance when processing is performed with automated developing stations which are part of processing lines. Due to short processing cycles the times allowed for development in some cases are well below 30 seconds.
3. The resistance to overdevelopment should be good, i.e., in case of positive processing, the unexposed layer areas should not be attacked by the developer; in case of negative processing, the exposed layer areas should not be attacked by the developer and in the case of reversal processing, the exposed and heat-treatedlayer areas should not be attacked by the developer. This ensures that, even in the case of repeated development, for example, in the course of photocomposing, the image is not damaged. Furthermore, even relatively old copying layers can be satisfactorily processed.
4. During development foaming should not occur and deposits should not form. These soil a developing apparatus, necessitating increased expenditure for maintenance.
5. The gradation, which is strongly influenced by the type of developer employed, should be as steep as possible. This makes improved dot reproduction possible with both positive and negative processing.
It is generally very difficult to provide a developer which fulfills all of the above requirements, particularly for reversal processing. EP 101,010 (=U.S. Pat. No. 4,530,895) discloses an aqueous-alkaline developer solution which contains silicate, benzoate and quaternary ammonium hydroxides and which results in a steep gradation following development. However, this developer impairs the hydrophilic character of the substrate material if used to develop printing plates, making its application very problematic.
DE 32 23 386 (=U.S. Pat. No. 4,374,920) and U.S. Pat. No. 3,586,504 disclose the addition of non-ionic surfactants, such as fatty acid amides or ethoxylated alkanols, alkyne diols and phenols, to the aqueous-alkaline developer solution. When developer solutions of this kind are used, steep gradations and short developing times are achieved, but the formation of deposits of layer constituents causes the problems described above.
EP 178,495 describes a multi-stage process for developing irradiated, radiation-sensitive, positive-working layers containing quinonediazide sulfonic acids and alkali-soluble resins, wherein the irradiated layers are treated with aqueous-alkaline solutions containing a fluorocarbon or a carboxylated surface-active agent. The carboxylated surfactants also include (poly)glycols etherified with a fatty alcohol and with hydroxyacetic acid, hydroxypropionic acid or hydroxybutaric acid.
The aqueous-alkaline developers disclosed in EP 178,496 and EP 209,153, which are based on O-fatty alkyl-O'-carboxymethyl-(poly)ethylene glycol, and the aryl ether sulfates disclosed in DE 39 15 141, provide excellent developing results. However, these developers exhibit an unacceptably strong foam formation.
EP 279,630 discloses a developer for positive-working and negative-working copying layers which are based on quinonediazides or diazonium salts, respectively. The developer comprises a substance showing an alkaline reaction, a reducing agent, a non-ionic or cationic surfactant and an aromatic carboxylic acid, such as, for example, benzoic acid, which may be substituted on the aromatic ring. The content of non-ionic or cationic surfactants leads to the same impairments during processing as described above. The publication does not disclose the use of the developer in reversal processes.
EP 274,044 is directed to a developer solution which is suited, in particular, for the processing of reversible reproduction layers. The developer solution contains, as essential constituents, alkali, an ethylene oxide/propylene oxide block copolymer and optionally a phosphate ester in order to prevent the formation of deposits. This developer composition gives good results even when reversible copying layers are processed. However, the amount of phosphate ester required effectively to suppress the formation of deposits causes foaming of the developer solution, and hence the composition of the developer is not ideal.